1. Field of the Invention
The present invention relates to improvements in relatively sophisticated lighting control systems of the type used most often in commercial settings for controlling the luminous output of a large number of lighting fixtures which are grouped together in some manner to define various "zones" of light.
2. Description of Related Prior Art
In many commercial lighting applications where large numbers of lighting fixtures (say, for example, several hundred) are used to illuminate areas of interest, it is common to group the fixtures in such a manner as to define "zones" of light which can be independently controlled from one or more wall-mounted control units. The wall-mounted control units are typically located in the vicinity of the lights they control. Each control unit usually comprises an array of manually manipulatable zone-intensity or "dimming" actuators, such as sliders or up/down push-buttons, each actuator being specifically assigned or dedicated to a particular lighting zone. Manipulation of any one of these actuators serves to vary a characteristic of a lighting control signal transmitted by the control unit and used to control the output of one (or more) dimming circuits or modules, hereinafter referred to as "dimmers," which apply power to each of the lighting fixtures defining a particular lighting zone. In addition to providing a means for adjusting the instantaneous light level of several zones of light, each control unit is usually adapted to store preset values for each of the lighting zones controlled by its respective actuators. In response to the actuation of any one of several "scene-select" switches on the control unit, stored preset values can be simultaneously recalled for all of the lighting zones, thereby creating any one of several different lighting scenes in the area illuminated by the preset lighting zones. Such multizone, multi-scene lighting control units are commercially available, for example, from Lutron Electronics Co. Inc. under the registered trademark "Grafik Eye".
As noted above, it is common to locate the lighting control units in the vicinity of the lighting fixtures they control. The dimmers through which they control power to the fixtures, however, are usually mounted in a centrally located power cabinet which is remote from the control units and lighting fixtures. Communication between the control units and the power cabinet has been achieved by a digital communications link in which the control units sequentially transmit, in a multiplex fashion, zone-intensity information on a low voltage communications bus. The multiplexed information is decoded in the power cabinet by a microprocessor forming part of a dimmer control panel circuit which controls the operation of the dimmers. Upon decoding the multiplexed zone-intensity information and determining, for example, through an appropriately programmed look-up table, which of the dimmers is to receive and act on certain zone-intensity information received by the microprocessor, the dimmer control panel circuit transmits such information to the appropriate dimmers. While it is known to transmit this data to the dimmers on wires connecting each dimmer to the dimmer control panel circuit, it is also known to multiplex such transmission on a digital communications link. In the latter case, each dimmer is assigned a unique binary (or digital) address code, and it responds only to zone-intensity information on the link that is preceded by (or somehow associated with) its respective address code. A microprocessor associated with each dimmer processes the address and zone-intensity information and outputs a dimming control signal which is used to control the firing angle of a triac or the like, thereby adjusting the RMS voltage applied to the associated lighting load and, hence, its luminous output.
In the past, "digital" dimmers of the above type have employed either an array of bi-stable "DIP" switches or one or more multi-positional rotary selector switches to define the unique address code of each circuit. See, for example, the digital dimmers made by Lite-Touch Inc. In the case of the bi-stable DIP switches, for example, the binary address code of each dimmer is set during system installation by moving a small switch actuator on each switch of the array to one of its two stable positions. It will be appreciated that, in the event that one or more of the dimmers needs replacement, the system user is required to manually set the state (or position) of the address switches of the replacement dimmer to assure that the replacement dimmer responds only to the zone-intensity information intended for the dimmer that has been replaced. Should this detail be overlooked or not understood, a service call may be required to correct the situation.
In addition to the digital addressing problem noted above, multizone lighting systems of the above type are notoriously difficult to modify (e.g., add dimmers or change the assignment of zone-intensity actuators) once the system is installed and operating. It will be appreciated that, during set-up and check-out, written documentation is always available to correlate each dimmer with the zone-intensity actuator that controls its output. Such documentation is usually in the form of a listing that assigns each dimmer to a particular zone actuator. This listing is desirable when it comes time to program the dimmer control panel circuit's look-up table that correlates the individual zone-intensity actuators with the dimmers. Should this documentation be unavailable or not readily understood at the time when modifications or additions to the system are required, a great deal of time can be expended in determining what actuator controls what circuit, and what symbology was used to identify the zone actuators so that re-programming of the look-up table can be carried out. Say, for example, a lighting system comprises three wallbox control units, U1, U2 and U3, disposed at different locations within a lighting region, and each control unit is capable of controlling six lighting zones through the manipulation of six zone-intensity actuators A1 through A6. Further assume that the system comprises 24 dimmers which control power to the various lighting fixtures of the system. In programming the dimmer control panel circuit's look-up table, it is necessary to assign each zone-intensity actuator to one or more dimmers. To conserve memory space, this programming is effected by using some abbreviated symbology, such as "U2,A3" and "D19" to identify a particular zone-intensity actuator and its assigned dimmer circuit, respectively. Should one desire to add a new dimmer to the system, one must not only possess the apparatus required to effect re-programming, but also one must have the knowledge of the symbology used in programming the power panel. Even having this information, the system user would then have to know how to program the power panel, a daunting task for all but a few. Ideally, the user should be able to add a new dimmer without need for consultation and/or assistance from the system installer.
A further problem associated with multi-zone lighting control systems of the above type is that of providing an efficient and low-cost means for dissipating the substantial levels of thermal energy generated by each of the dimming circuits so that a large number of such circuits (e.g., 24) can be housed in a relatively compact space. As noted above, each dimming circuit includes a power switching device, e.g., a triac, which serves to interrupt the line voltage applied to a lighting load for a preselected period during each half-cycle to control the RMS voltage across the load. It also includes a relatively large choke or coil which forms part of a radio frequency interference (RFI) suppression and lamp de-buzzing network. When the dimmer is operating, both of these components heat to temperatures well in excess of 100 degrees Centigrade and act to irradiate the other components of the dimmer module. To assure proper performance of the dimmer, it is common to thermally couple the power-switching device and RFI choke to a relatively elaborate heat sink, e.g. an aluminum plate with heat-dissipating fins. Further, it is common practice to either select the other dimmer circuit elements for their ability to withstand and operate under high temperature conditions, or to provide sufficient spacing between the heat-generating components and other components. As may be appreciated, these temperature-compensating measures tend to add significant cost to the lighting control system, and/or enlarge the physical size of the dimming panel, i.e., the structure that supports multiple dimming circuits.
Additional drawbacks of existing digital dimmers of the above type are: 1) the dimming circuits are not easily by-passed to provide emergency or temporary lighting in the event of a loss of the dimming control signal; in such event, jumper cables are usually used to by-pass or shunt the dimmer and thereby connect the lighting load directly to the line voltage; 2) their voltage compensation circuitry is tailored for different nominal line voltages (e.g., 110 or 277 volts), thereby requiring different dimmer circuits for different localities; and 3) they can be difficult to trouble-shoot in the event of system or component failure.